The present invention relates to rotary actuators with clutching and declutch mechanisms that enable the output member to be rotated by a hand wheel in the event that operation of the drive motor is temporarily interrupted.
The primary drive mechanism for the rotary actuator is an electrical drive motor. During utilization of the actuator, however, a secondary drive mechanism must be provided in case of the occurrence of a power failure, failure of the motor, or the need of manual adjustment. Often during the initial startup of the equipment that is being operated by the rotary actuator, it is desirable to be able to operate the actuator manually before placing the motor into operation. In order to accomplish all of these purposes, a secondary source of power, a hand wheel is provided for manually rotating the actuator.
A clutch mechanism and a declutch mechanism are provided for switching the rotary control of the actuator between the drive motor and the hand wheel. While both rotary actuators per se and clutching and declutch mechanisms incorporated in such actuators are well known in the art, the various devices that have been provided are relatively complex which increases both the cost of manufacturing and maintenance of such equipment.
A problem can occur in certain employments of clutching type rotary actuators when a valve, winch, or chain drive to which it is attached exerts a torsional force back through the drive members. In such situations when the back drive force is not continuously reacted by members within the actuator the attached load will shift. If the actuator can not react against such torsional force as in the case of a winch an attached load can fall, or in material transfer operations, a gate valve can close accidentally. These situations can occur when the clutch mechanism has a neutral position through which it must pass between the powered position and the manual hand wheel operating position.
Another problem which can occur during a manual mode of operation arises when continuous or intermittent torsional forces are exerted on the power output member of the acutator. The problem is that the back drive force can cause the hand wheel to begin to rotate when the clutch is in the manual mode position. Depending upon the load requirements and criticalities this could represent a dangerous condition. This of course permits uncontrolled movements of the equipment operated by the actuator when an operator is not controlling the hand wheel.
Also exemplary of the current state of the art of rotary actuators with declutch mechanisms is U.S. Pat. No. 4,022,309 to Denkowski et al. The valve operating mechanism disclosed by this patent includes both motor and manual drive devices for driving an externally threaded drive stem. The driving force is applied through a worm shaft and a worm to a worm gear. The worm gear has upstanding lugs that engage a pair of lugs that extend downwardly from a motor clutch ring. The clutch ring through a pair of detent rollers arranged within a plurality of corresponding slots drives a cup shaped drive ring that is positioned in the motor clutch ring. The lower portion of the drive ring is connected through splines to the drive sleeve. The drive sleeve in turn is internally threaded so as to be engaged with the externally threaded valve stem. When the motor power is either intentionally deactivated or a failure has occurred, the actuator mechanism can be declutched so as to switch between the motor mode of operation and a manual mode of operation. A crank or a lever can be manually rotated so as to turn a pinion declutch shaft. Secured to the declutch shaft is a pinion that has a fixed number of teeth arranged in engagement with circumferential grooves on a clutch sleeve. Arranged below the clutch sleeve is a lug ring. That lug ring is supported in an annular floor of a drive ring. The lug ring has a pair of opposing slots that are located to receive downwardly extending legs of the clutch sleeve. A pair of opposing lugs, which are spaced 180.degree. apart, extend radially outwardly from the wall of the lug ring. Lugs are located in the upper half of the lug ring wall. In the lower part of the lug ring wall are a pair of recesses which serve to receive the detent rollers.
Numerous other patents disclose various embodiments of rotary actuators many of which have clutch and declutch mechanisms for alternatively coupling the output member to an electrical motor or a hand wheel. Exemplary of such actuators are those illustrated in the following U.S. Pat. Nos. 2,694,320 to Kron; 3,168,841 to Caldwell et al.; 3,198,033 to Fry; 3,257,866 to Fry; 3,279,276 to Fry; 3,298,249 to Nott; 3,585,867 to Grimshaw et al.; and 3,603,175 to Horton.
U.S. Pat. No. 4,393,965 issued to the inventor hereof describes and claims a rotary actuator which has a neutral clutch position and in which an attached torsionally back force can cause the hand wheel to freely rotate under an imposed back force when in the manual operating mode position. The disclosure of that patent is hereby incorporated by reference as though fully set forth herein.
These patents do not recognize the above enumerated problems arising from back drive force from the loads when not reacted by the actuators. Consequently, the problems which can arise from the availability of neutral clutching positions and hand wheels which can free wheel under torsional loading forces were not considered in actuators of the type herein described.